The biblical quote is from Deuteronomy 31.6:
Be strong and courageous. Do not be afraid or terrified because of them, for the Lord your God goes with you; he will never leave you nor forsake you.
This verse comes at the beginning of the aged Moses' third address to Israel. Banned by God from crossing the Jordan to enter the Promised Land, Moses appoints Joshua as his successor to lead the people against their enemies, enjoining him to "be strong and courageous". The Catholic humanist Erasmus called Thomas More an "English Socrates", recalling in that epithet the courage of conscience manifested by the Greek philosopher. Erasmus might also have designated More as an 'English Joshua' for his willingness to venture against death. Yet there is something greater than Joshua here. Joshua was a warrior, and as such he was called upon to risk death for the common good, the happiness and security of his people. The same could be said today of the soldier and the police officer. But Thomas More was singled out in his time to act against his conscience. As a leading member of the aristocracy, More was expected his to add his assent to Henry VIII's Act of Supremacy, making the king the head of the Church in England. If More consented, he would live. If he refused his consent, he would die. As the 'king's good servant, but God's first', More acted on his conscience and chose martyrdom, which the Fathers of the Church understood as a kind of baptism. These same Fathers also understood the sacrament of Baptism as prefigured in the crossing of the Jordan River by which the People of God received the gift of the Promised Land, an image of eternal life.